Building a DM-1 Mast (Dirk Schwenk)

Jet-14 Mast Set-up Guide
Circa 2000
Editor's Note: Since I wrote this article in 2000, the DM-1 has truly become the Class standard, and there are many people that have built lots of rigs. This is a good starting place if you are going to do so, but don't forget to talk to the real experts, like Greg Koski, Brent Barbehenn, Bob Putnam, Mike Parramore, and Dave Michos.


Part I: Getting the Hardware

Last year I had the opportunity to build two DM-1 masts from bare pole
to completion. Its not too hard, but it does take some time. This
series of articles will guide you through assembling the hardware,
putting it all together, and finally tuning it up. The key with the
DM-1 is build it STRONG. If you don’t, it will come down. Minimize the
holes that you cut, and make sure that your pop rivets are stainless
steel and of sufficient diameter. I failed to fully heed this warning
with my first mast, and I’ve never been able to match the speed I had
before it broke.

Before you begin, I recommend that you make a diagram (or use one from
the class rules) that shows exactly what parts you intend to put where.
This takes a little time in beginning, but will save time in the long
run. The key question you will face is whether to run your halyards and
controls internally or externally. I chose to go outside with
everything on my second mast because it takes a lot less time, its
easier to inspect the lines and you end up with far fewer holes in your
mast section. Many people go internal because it reduces windage and
looks much better. Most people do not put the spinnaker halyard
internal, however, as this requires a hole in the unsupported upper
section of the spar.

In order to begin, you will need:

1. A copy of the class rules, with the mast diagram--it contains all necessary measurements. If you are confused, there is an article discussing this topic in Jet Blasts before last years Nationals.

2. A DM-1 mast section. There is a $75 shipping fee so try to order with a group to spread the cost, or go pick it up when you’re in New England. When I ordered, I ordered with a group through Mike Parramore, as he gets a dealer discount. You can check with Greg Koski about this as well.

Dwyer Aluminum Mast Co.
2 Commerce Drive
North Branford, CT 06471
(o) 203-484-0419
(f) 203-484-2014
Website address: I don’t have it handy, but its on the web.

3. When you order, get the following parts from Dwyer

  • Section: 22 feet (check this against your old mast) (about $175).
  • Mast butt: Part # D 212 (about $7.00).
  • Sail feed slot: cut it 56 inches from the end (check this against your old mast) (about $6).
  • Hound fitting: (where the shrouds attach to the mast) I don’t have the part number, but specify that it fit the DM-1 section. (about $20).

4. Spreader assembly (Including spreader bracket and airfoil

a. I believe that Dwyer has a spreader bracket and airfoil spreaders
available for the DM-1. This will be the easiest option by far. Get a
bracket that fits the DM-1 and wraps around the front of the mast, as
opposed to one that comes in two different pieces. Get airfoil
spreaders that fit the bracket. Most top boats have spreaders between
17 and 18 inches (measured from the mast to the tip of the spreader).
Order 20 inches and cut them accordingly--after you can measure with the

b. I personally did not get Dwyer spreaders, as I wanted to have
spreaders where you can adjust the angle and the length. (I couldn’t
find anyone that really knew what the angle or length should be, so I
didn’t want to assemble them permanently until I could test my own
settings). Instead, I got Proctor pieces at Annapolis Performance
Sailing (800-729-9767) and customized them to fit the Dwyer section.

  1. Proctor extendible, adjustable spreaders (Part # PR009) (about $75 per pair).
  2. Spreader lug for adjustable spreader (Part # PR 020) (about $22 per pair).
  3. Front wrap spreader bracket (Part # PR019) (about $20)

5. Main halyard assembly

a. Dwyer offers a main-halyard block for the DM-1 (Part # D 101)
(about $14). I personally felt that it was too high profile, and I
didn’t like the idea of nylon sheaves. Without question, however, this
will be your easiest and cheapest alternative.
b. I chose to go with two through-blocks, one through the front of the
section, and one through the wall underneath the sail track. As
discussed below, this requires much more work, including hack-sawing off
several inches of sail track. If you go with this option, get the
smallest available through blocks. If you anticipate using wire for
your main halyard (I used Vectrus 12 (Vectran) line), make sure you find
blocks which are designed to handle it.
c. If you choose to run your main halyard internally, you can just go
with one through block at the top, and cut a hole down low.


6. Miscellaneous:

A quick list to consider, some of these things you can probably strip
from your old stick, otherwise, talk to APS or some other knowledgeable
hardware outlet.
a. Halyard lock: I put mine at the top of the mast to decrease
bowing--its a hassle to get the sail down though.
b. Spinnaker halyard block and fitting: you want a flat thing with a
loop on it to hang the block from.
c. Jib halyard fittings: through block if you’re going internal. If
not, block and shackle to hang from the hound fitting. Consider how you
intend to cleat or control the halyard to determine your other fittings.
(I have mine to a magic box so I can control tension).
d. Topping lift block and fitting.
e. Chafe collars: I mounted my spreaders over a Proctor (blue) chafe
collar (Part # PR 032, about $20). You have to custom bend them to fit
properly. I recommend putting a chafe collar at the spreaders, the deck
and the butt if you have internal controls exiting there. Dwyer also
sells a what it calls a mast splice that serves the same purpose. As I
understand it, they go internally, but I’ve never used them.
f. Boom vang bail or tang: there are a variety of options here. I
used a basic bail and bent it to fit around the chafe collar.
g. Mast butt block: If you go internal on your halyards and controls
you may want to consider a multi through block for the base of the mast.
You may also want to consider halyard exit plates instead.
h. Stays: I don’t know how anyone figures out how long they should be
before they put the mast up, but good luck. The Dwyer hound fitting
requires a thimble-eye for the upper end of the stay-- you can use your
old fittings at the deck.

Part II: Finishing the Mast

As I mentioned before, the chief concern here should be that you build
a strong mast. The basic tools that you will need are a tape measure,
magic marker, power drill, set of metal files, hacksaw and a top quality
pop-rivet gun that can pull stainless steel rivets. Before you begin,
you will also need to borrow or make a c-shaped thing to measure the
distance from the bottom of the keel to the black band above the deck.
Again, this is beyond the scope of this article, but look at Ralph
Hanson’s article from last summer. Your local measurer should have one.

The most time consuming part of building the mast is cutting the holes
for through-fittings. I approached it by marking the outline of the
fitting with a pen, then perforating inside that mark with the drill.
Once perforated, I broke the piece out, then filed the hole to size
using an appropriate size file. This will go fastest if you have a few
small files and some larger ones. I have heard of people using a router
to cut the holes, but I never tried it.

Step 1: Measurement: Place the plug in the bottom of the mast, put the
mast up and make your initial band above the deck. Check this about
twenty times, because if its wrong, you’ll have to do everything over.
Use that to measure and place the other bands. Then mark the spot where
you will put the spreaders, jib halyard block, topping lift, etc. I
riveted the plug on later so I could get all of the aluminum shavings
out. I also drilled holes in the bottom so that the mast will drain.

Step 2: Main halyard: If you use the Dwyer fitting, just pop it on,
drill some holes and pull the rivets. If you use a through-block, you
will need to use a hacksaw to saw off about the first five inches of
mainsail track, before starting the hole for the fitting. I put my
halyard lock about six inches below the top of the mast. This reduces
the tension on the spar when its breezy, but it makes it more difficult
to get the sail down, particularly when you’re away from the dock.

Step 3: Spinnaker Halyard: Pretty self explanatory. I used a rotating

Step 4: Hound fitting: I strongly recommend the Dwyer hound-fitting.
The most difficult thing about it is that you have to drill a large hole
through the center of the section. I found it difficult to get the hole
level. After screwing it up, I used a round file to file one side lower
so that the two sides were approximately even.

Step 5: Jib Halyard: On my second mast, I simply hung the external
block from the hound fitting, so that the halyard and forestay attach at
approximately the same point. On my first mast I went internal. If you
do the same, be sure that the block be as near the hound-line as
reasonably possible.

Step 6: Spreaders: This is the most complicated part, and the part that
failed on my first mast. I think that my problem was that the rivets
that I used had a head that was too small. The spreader bracket pulled
over the top of them (we were going downwind with the kite up), and the
spreaders blew forward. The second time, I took a blue proctor chafe
collar, and bent it down so that it takes a lot of force to snap it over
the section (I beat it with a hammer, the darn things are pretty stiff).
I mounted the spreader bracket over the chafe collar, then riveted the
spreaders onto the whole thing. If you are using fixed spreaders, it is
my understanding that you can drill multiple holes in the spreaders, so
that you can drop the pin in at different places. If you are using
adjustable spreaders, you will also have to drill and place the lugs.
There’s not too much room to do this so plan carefully. Most boats have
their spreaders between 17.5 and 18 inches measured from spar to tip. I
think mine are 17 7/8 inches. I had to use the hacksaw to get them the
right length.

Step 7: Deck: put a mast chafe collar where the spar goes through the
deck. Put a vang tang or bail as low as you can, and make sure the bail
is bent down so that it doesn’t hook your sheets.

Step 8: Halyard Exits: If you use internal halyards, figure out how to
get them back out as is appropriate for the set-up of your boat.

Step 9: Rig it: halyards, stays etc.

Step 10: Make sure that there is nothing sharp anywhere on the spar. If
so, file it down or wrap it with rigging tape.

Step 11: Rig the boat in your yard and figure out what doesn’t work.
Fix it.

Part III: Tuning the Mast:

Once you have completed the mast, you probably want to know how to get
it tuned up nicely. I definitely don’t have the final answers on this
issue, but you can bring my article to real class studs like Koski,
Barbrehen, Simonds or Bill Buckles, and they can tell you what I do
wrong. I do suggest that you keep a log of the settings that you use
each day of racing, so that you can test and recreate settings over
time. This is only way to know whether that 1/4 inch change in rake is
going to drive you to victory or spit you out the back.

Step 1: Set the butt. Long-time Jet wisdom says that the butt of the
mast should be 19 inches in front of the centerboard pin. Recently,
there has been some movement to try setting it further forward, as Brent
Barbrehen does. If its between 19 and 19 5/8, you're probably fine.

Step 2: Set it at the deck: Be sure that the hole in your deck is in
the middle of the boat, and directly above the mast step. If you are
going down from a DM-2 or a wood mast, you will probably need to build
up the sides of the hole anyway, so get it straight.

Step 3: Make sure its in column: Tighten the shrouds a little bit and
run tape measure up your main halyard.
First, sight up the sail track and make sure that the mast isn’t bowing
to either side. If it is, it may be a problem at the deck, with the
length of the spreaders or angle of the spreaders, or with the relative
length of the shrouds. If it looks like the problem is at the
spreaders, make sure your spreaders are the same length and that they
are coming off the spar at the same angle. Take the mast down and stare
at it for twenty or thirty minutes if you can’t decide. (Well, that’s
what I do, anyway). If it appears that the problem is at the hounds, be
sure that you have the shrouds the same length, and that you hounds pin
is level in the mast.
Second, measure the distance between the tip of the mast and deck just
aft of the shroud attachment. If this measurement is not within a
quarter of an inch, adjust the stays, if possible. In any event, get it
as close as possible to even.

Step 4: Set the rake and tension:
The object here is to get the rake right, while getting the shrouds at
the right tension. Since most people tension using the forestay or jib
halyard (which pulls the mast forward and decreases rake), this is a bit
of a balancing act. I measure the rake from the tip of the mast to the
top center of my transom. If you have a glass boat, your transom may be
lower, so adjust the numbers accordingly. Most competitive Jets sail
with their rake between 20 feet 9 inches and 20 feet 10 inches. I set
my boat up so that it is at 20 feet 8 3/4s with minimum tension (about
75 pounds). I then tension my jib while under sail, which presumably
pulls the mast tip forward. Most people sail with tension of between
100 and 200 pounds on the side stays. I haven’t found any speed benefit
from more tension, but you might try it in a blow.

Step 5: Set the bend:
This step is pretty optional. When you pull on jib halyard and
mainsheet tension, the spar bends in funky ways. It is difficult to
predict these changes without looking at them. If you have time (which
I never seem to), strap your boat to the trailer and run the sails up.
Tension the jib and main and look at the mast. I try and set up the
boat so that there is nice even curve through the entire spar. This
means restricting the forward bend at the deck somewhat--I have a mast
ram for this. T-blocks that drop into the slot, or a line that runs
around the front of the mast will also work. If you have adjustable
spreaders, you can restrict bend by moving the spreaders tips forward,
encourage it by moving them back. Don’t go too far either way, however,
as this creates high loads.

Step 6: Go sailing and whip some butt.

Dirk Schwenk

Since I wrote the article about rigging and tuning a DM-1 I have learned

two things that should be passed along.

1. Class-veterans, notably Ralph Hansen, stress the importance of

through-bolting the speader bracket, instead of just riveting it onto the

mast. Most brackets will not accept a bolt that is straight, so you have to

bend it. This is not as hard as it seemed before I tried it. I just took a

stainless bolt, stuck it in a hole in my trailer, and bent it until it fit

through--it took about ten minutes.

2. I just bought a dremel-type tool that has an attachment for little stone

cutting discs--these work great for cutting the mast walls for

through-blocks, etc.

Dirk Schwenk

Jet 398

Upcoming Events

Su Mo Tu We Th Fr Sa
1 2 3 4 5 6 7
8 9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31
Show Full Calendar